


Day Eight

by FellQueen (Nikasha)



Series: Kinktober 2019 [8]
Category: Undertale (Video Game)
Genre: Abuse, Alternate Universe - Dreamtale (Undertale), Alternate Universe - Xtale (Undertale), Cross!Sans - Freeform, M/M, Masochism, Nightkiller - Freeform, Nightmare!Sans - Freeform, No Aftercare, Sadism, Tentacle Sex, Tentacles, killer!sans
Language: English
Status: Completed
Published: 2019-10-09
Updated: 2019-10-09
Packaged: 2020-11-28 03:58:12
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,408
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20960096
Author URL: https://archiveofourown.org/users/Nikasha/pseuds/FellQueen
Summary: Day EightPrompt: TentaclesPairing: KillerNight (Killer!Sans/Nightmare!Sans)





	Day Eight

**Author's Note:**

> I had a rough day.
> 
> It isn’t rape, but it skims very close. If I missed any warning tags, please let me know! That goes for all these one-shots.
> 
> Enjoy!

“Killer!”  
The skeleton jumped a step in his already hurried pace, startled by the booming voice. He tried not to look too overeager as he trotted up to the dark throne in the middle of the room, but it was pretty much a lost cause.  
A quick glance around and he realized no one else was in the room. Odd, if exciting. Dust was known to lurk in the corners if he sensed trouble.  
Killer stopped in front of the throne, darkened sockets giving the dripping black form sitting on the stone a thorough look. He shoved his hands in his pockets and slouched, grinning indolently. “Sup, boss?”  
Nightmare was already scowling, but that wasn’t exactly unusual. He leaned forward, resting his elbows on his knees, and narrowed his eye. “You think this is funny?”  
Killer ran through all the scenarios of previous events that might have irked the king quickly and came up empty. “Depends on how punny it is, boss.”  
The tendrils behind Nightmare twitched and Killer involuntarily glanced at them. They were coiled up, poised to strike like angry snakes. Not a good sign.  
“I told you not to kill the monsters in that ‘tale universe,” he said. His voice oozed and dripped like the darkness on his body, pitched low. “You disobeyed me.”  
Killer felt a chill go down his spine and he shifted his weight. “I know, but I hadn’t had a LV boost in ages, and it felt so _good_ and it made the mother scream really loud, so I thought—“  
“You didn’t think,” Nightmare hissed, expression tightening into a grimace. “I had a plan for that little girl already, and now it can’t be put into action.”  
Shit. “S-Sorry. We can use another kid, though, right?” He grinned nervously.  
Quick as the snakes he had compared them to before, the tentacles shot forward and latched onto him, finding a hold on his wrist and femur, then tugging him closer until he was almost touching Nightmare. He swallowed, soul pulsing an angry red that gave Nightmare’s slime an unearthly shine.  
“There’s no ‘we,’ you worthless creature,” he said coldly. He straightened and leaned back in the throne, crossing his ankle over the opposite knee. “You follow my orders. Nothing more. Nothing less.”  
“G-Got it.” Killer flinched as a third tentacle began toying with the hem of his shirt. He squirmed. “Uh, what are you doing?”  
Nightmare finally did smile. “Feasting.”  
Killer flushed blue, embarrassed and a little interested. The tendril slipped under his shirt and began coiling through his ribcage, leaving behind oily residue that clung stubbornly.  
He gave a soft laugh. “You know you can always just as—“ He choked on his words as the tentacle that had been crawling around inside him jolted up to wrap around his vertebrae, then flirted with the hollow under his jaw.  
“I don’t ask,” Nightmare said almost pleasantly.  
Killer whined as he was lifted off the floor, struggling against the pressure on his spine. His wrist and femur were still bound as well, but Nightmare seemed to be purposefully resting most of his weight on the coil around his neck.  
It hurt. It felt like he was going to break. He tried to scream and just rasped, free hand coming up to tug at the dark magic.  
He felt something wrap around his soul.  
“I know you,” Nightmare sighed, leaning his head in his palm. “You could escape if you wanted.” He smiled. “You don’t want to.”  
Killer gagged, jerking in his grasp. The tentacle on his soul curled around it, hiding it from view, covering it in darkness. His free leg kicked at the air.  
Nightmare squeezed.  
Killer froze, shaking visibly. The coils loosened and he slumped. Black seeped from his sockets.  
“Better,” Nightmare said. “Give me more, Killer. Give me your pain.”  
Killer whined again. He was still held in a painful grip and the touch on his soul was anything but pleasant, but he wasn’t actively being choked anymore. He could feel the tendril flirting at the back of his teeth like a second tongue and jerked as if he could escape.  
Nightmare laughed at him.  
His chest felt tight like there was a coil around it, and his breath came out in sharp pants. Every thought was quick and fleeting, mostly of how it was very possible he was about to die.  
He wouldn’t mind.  
Killer suddenly felt another tendril slip into his pants and down into his pelvic cradle, sliding around. He instinctively tried to get away, but after the first attempt, he forced himself to relax.  
It was fine.  
His magic crackled and shifted into place. The tentacle moved away, like Nightmare was startled by it, then shifted to begin tentatively poking and prodding at the sensitive tissue.  
Killer sighed.  
Suddenly it reoriented and shoved deep into Killer’s cunt. He screamed, struggling wildly. “Fuck! Fuck!”  
Nightmare was surprisingly silent during that, and Killer was too blinded by searing pain and overwhelming fullness to look. He slumped against the tendrils’ hold, sucking in ragged gasps of air.  
“Good.”  
Killer flinched like he’d been struck. The word meant nothing to Nightmare, a throwaway trinket, but he knew it meant a lot to Killer. You couldn’t call what flowed through him a positive emotion, per se. It was a mix of resignation to this torment, obsessive loyalty, maybe something like love. But his love was the kind that would lead to stabbing in the back, blood on boney hands, the thorns of a dead rose.  
No, you couldn’t call it positive at all.  
Killer’s breath hitched as the magic deep inside him twisted, not thrusting so much as pressing against every available surface and sliding against it. He shuddered and clutched weakly at the tentacle still around his neck. His cheekbones were almost solid black from what flowed out of his sockets. It dripped from his jaw down to the floor.  
The tendril moved again and Killer moaned. The sharp pain was edged with the beginnings of pleasure. The sensation was such a relief, it was heightened.  
Nightmare was still quiet and unmoving on his throne, dark eye focused on the struggling skeleton he held aloft. He huffed softly, amused.  
The slick sounds of Killer getting wet and the goop dripping to the floor were loud. The white skeleton was now almost black, covered in Nightmare’s ooze. Killer twitched and spread his legs wider.  
The tendril wrapped around his soul squeezed down. Killer screamed again, going rigid as pleasure-pain shot through him like lightning. He was locked in tension like his body was trying to shake itself to pieces.  
The coil loosened again. The one between his legs slid free, sludge and blue cum following its exit and splattering across the floor. Killer was held in the air for a brief moment longer before abruptly he was released. He hit the floor with a loud clatter, yelping in shock.  
He laid there in a heap, shuddering and covered in various liquid. He was pretty sure his arm had cracked in the fall. Maybe the wing of his pelvis, too, but that area already was chock full of agony and he wasn’t sure.  
Nightmare let him lay there for a moment, surprisingly benevolent. When Killer weakly shifted to look at him, there was a hazy, satisfied aura to him. The negative emotions of a single tortured individual would never be enough, but it took the edge off for a bit. Probably. It explained the mild kindness of letting him rest a moment.  
“Get up.” Nightmare sighed, one tentacle flicking and sending blue and black across the stone flooring. He grimaced. “Clean this shit up.”  
Killer didn’t wait to be told twice. He shakily moved to his knees, wincing as the pressure sent a stabbing pain through his arm. Then he stood, wobbling uncertainly. “I c-can’t...”  
Nightmare stared him down, going unnaturally still. “Did you not learn your lesson?” he asked. At the very edge of his tone, he almost sounded excited.  
Killer shrank back, though. He wanted to please Nightmare, but he could only take so much. “Sorry.” He started limping his way towards the back, behind the throne, where they kept cleaning supplies. When he returned, Nightmare was gone, but Cross was there, chewing idly on a chocolate bar. The mess on the floor was gone.  
Cross didn’t say anything. Neither did Killer.  
He took a shortcut back to his room.

**Author's Note:**

> List used: https://twitter.com/idek_uggy/status/1178349575725174786?s=21
> 
> Tomorrow is -looks- oh eh not that. Let’s do sensory deprivation instead!


End file.
